1. Field of Invention
The present invention relates to a lamp driving device and method. More particularly, the lamp driving device and method relate to generating several phased signals that have different phases and no overlapping pulses.
2. Description of Related Art
With the rapid development in technology, flat panel displays (FPD) with the advantages of high image quality, compact size, light weight, low driving voltages and low power consumption have become very popular for incorporation into electrical devices and have become the mainstream display apparatus. For example, the FPD can be introduced into a portable TV, mobile phone, video recorder, computer monitor, and many other kinds of consumer electronics.
In the FPD, the backlight module is used as the light source. A lamp driving device in the backlight module is used to drive several cold cathode fluorescent lamps (CCFL), and to adjust the brightness of these CCFLs. FIG. 1 is a functional block diagram depicting a lamp driving device of the prior art. The lamp driving device 100 has a pulse width modulation circuit (PWM) 110, and several bridge circuits 141, 142, 143 and 149. The pulse width modulation circuit 110 is arranged to generate several driving signals 131, 132, 133, and 139. The bridge circuits 141, 142, 143 and 149 are coupled to the pulse width modulation circuit 110 and are arranged to respectively receive one of the driving signals 131, 132, 133, and 139, wherein each bridge circuit is driven by the received PWM signal. The bridge circuits 141, 142, 143 and 149 are respectively coupled to several transformers 151, 152,153, and 159 to individually adjust the output voltages of the bridge circuits 141, 142, 143 and 149. Furthermore, the transformers 151, 152, 153, and 159 are respectively coupled to one of the cold cathode fluorescent lamps 161, 162, 163, and 169. The lamp driving device 100 thereby drives several cold cathode fluorescent lamps 161, 162, 163, and 169 by the method depicted in the figure.
For example, the pulse width modulation circuit 110 of the lamp driving device 100 generates two driving signals 131 and 132. The driving signal 131 drives the cold cathode fluorescent lamp 161 by the transformation of the bridge circuit 141 and the transformer 151. The driving signal 132 drives the cold cathode fluorescent lamp 162 by the transformation of the bridge circuit 142 and the transformer 152. Therefore, the lamp driving device 100 can drive the cold cathode fluorescent lamps 161 and 162 simultaneously.
However, the driving signals 131, 132, 133, and 139 described above have the same waveforms and identical phases without phase differences. Thus, the lamp driving device 100 is encumbered with bigger instant output loading, and may generate heavier electromagnetic interference (EMI) that affects other electrical devices. Therefore, a lamp driving device and method to reduce the instant output loading and the electromagnetic interference is needed.